Semen and Seminal Fluid
From Encyclopedia of Sex and Sexuality
Semen is composed of seminal fluid (the material produced by the internal male sexual organs) and sperm (produced by the testicles). It is released during ejaculation. The volume of semen normally ranges up to a full teaspoon and is affected by the degree of sexual arousal and the frequency of ejaculation. In general, the volume of semen does not correlate with fertility or virility.
Semen is whitish in color and opaque. It usually has a distinctive odor, sometimes described as somewhat like that of chlorine bleach. It is usually ejaculated in a viscous state that thins as it liquifies over a period of twenty to thirty minutes. Most of the seminal volume comes from the seminal vesicles, which produce a gel-like coagulum. This coagulum is liquified by fluid produced by the prostate, that makes up the next largest component of seminal fluid. Together, these organs provide a number of chemicals and nutrients that support the function and motility of sperm. The smallest volume of fluid (about 3 to 5 percent of the total) provided to the ejaculate comes from the testicles themselves. This fluid is highly concentrated with sperm.
After a vasectomy (see Vasectomy and The Male Pill), when sperm from the testicles no longer reach the semen, there is no detectable difference in semen volume. Men who have had a vasectomy also have no change in the odor or color of semen, and ejaculation is unaffected by the procedure. The presence of sperm can only be evaluated by examining the semen microscopically. A small part of the seminal volume is also produced by the periurethral and bulbourethral glands. Some of this fluid may be released prior to ejaculation and is noticeable as a drop of fluid at the end of the penis during sexual arousal. Bulbourethral secretions are thought to cleanse and lubricate the urethra, the urine and semen passage, prior to ejaculation.
In men who are HIV-positive, preejaculatory fluid contains detectable levels of the HIV virus. Semen contains high levels of fructose and other substances necessary to nourish sperm, but it has no properties other than its ability to help support sperm function. It does not contain any proteins beneficial to the health or beauty of skin, nor is there any evidence that infrequent ejaculation has any adverse effects on a man.
Although sperm are highly concentrated in the first spurt of ejaculated seminal fluid, they may be found throughout the ejaculate and even in the pre-ejaculatory fluid. It is for this reason that withdrawal of the penis from the vagina just before ejaculation is not a reliable method of birth control (see also Safer Sex).
Some of the components of semen act on the female reproductive tract to “signal” to the vagina and uterus that it is time to transport sperm up into the female reproductive tract after intercourse.
